Cellulosic biomass is an abundant substrate for biofuel production. However, many microbes cannot natively metabolize pentose sugars abundant within hemicellulose. Although engineered Saccharomyces cerevisiae can utilize the pentose xylose, the fermentative capacity pales in comparison to glucose, limiting the economic feasibility of industrial fermentations.
At present, only a handful of Hemiascomycete yeasts are known to naturally ferment pentose sugars, such as xylose, that are abundant in hemicellulose. Although some aspects of xylose utilization have been uncovered in xylose-fermenting fungi, much of the mechanism remains unresolved. Xylose-fermenting fungi, including the well-known Pichia stipitis (Psti), are associated with wood-boring passalid beetles that may rely on fungal symbionts to release nutrients from wood. Other related yeasts do not natively ferment xylose, suggesting that xylose fermentation in these yeasts has evolved in a specific and unique fungal environment.
In view of the current state of the biofuel industry, particularly ethanol production based on xylose-containing feedstocks, it can be appreciated that identifying genes related to enhanced biofuel production is a substantial challenge in the field. Accordingly, a need exists in the field to identify additional genes that influence biofuel production in yeast, and consequently engineer recombinant strains of yeast capable of increased biofuel yields from commonly-available feedstocks, including xylose-containing feedstocks.